U.S. Pat. No. 993,530 and U.S. Pat. No. 2,313,387 disclose rotary compressors. Compressors configured in this manner are commonly used as vacuum pumps and as refrigeration compressors. Liquid lubricants perform several functions within a compressor. Lubricants reduce the friction between contacting components that are in relative motion with respect to one another. This reduces frictional heating and wear. For instance, surrounding the compression space of a compressor small leakage paths exist between adjacent parts that allow compressed gas at a relatively high pressure to leak to low pressure areas. This reduces the efficiency of the compressor. Liquid lubricants are able to effectively seal these leakage paths, thus, increasing efficiency.
In addition, the specific thermal capacitance of liquids is much higher than that of gases. Therefore, relatively small amounts of liquid lubricant in the compression space are able to absorb a relatively large amount of heat. When a gas is compressed adiabatically a substantial temperature rise of the gas occurs. During operation of a lubricated compressor, liquid lubricant, in the compression space can absorb some of the heat-of-compression. This decreases the temperature rise of the gas being compressed. Since compression work is directly proportional to gas temperature, the efficiency of the compressor is improved.
Liquid lubricants can also bear substantial loads, such that parts that appear to contact are actually separated by a thin film of lubricant even when the force trying to bring the parts into contact is substantial. Gases, on the other hand, support relatively small loads due to their low viscosity and high compressibility. Gases also leak much more readily from very small clearances.
In view of the benefits attributed to liquid lubricants in compressors, it becomes difficult to design an oil-less compressor that is efficient, reliable and cost effective to manufacture. Additionally, typical compressors suffer from other deficiencies that make them inefficient and noisy, they require increased power, and are subject to wear. The rotary compressors described herein solve these and other such issues.